Blast-room for abrasive blasting system

ABSTRACT

A blast-room for an abrasive blasting system having a floor with closeable scavenging ducts and end or cross draft ventilation. The floor is comprised of a plurality of parallel floor members that form elongated troughs or valleys with sloped sides to trap falling abrasive and waste particles. Between each pair of adjacent floor members and extending below their lower edges is a duct member having an elongated opening which is periodically closeable by a controllable closure means such as an inflatable valve member that provides an air-tight seal. At one end of the floor the ducts have small permanent openings to permit air to enter and their other ends are connected to a suction fan capable of creating a conveying air velocity in the ducts when the closure means has closed. During operation of the blast-room the closure means remains open for a period of time while a quantity of abrasive and waste particles are collected in the conveying ducts, then periodically the duct closure means are closed so that the conveying air can remove the particles from the ducts.

United States Patent Arnold [4 1 June 27, 1972 [54] BLAST-ROOM FOR ABRASIVE BLASTING SYSTEM Ted A. Arnold, Palo Alto, Calif.

[73 Assignee: Vacu-Blast Corporation, Belmont, Calif.

[22] Filed: Sept. 22, 1970 [21] Appl. No.: 74,341

[72] Inventor:

Primary Examiner-William E. Wayner Attorney-Owen, Wickersham & Erickson ABSTRACT A blast-room for an abrasive blasting system having a floor with closeable scavenging ducts and end or cross draft ventilation. The floor is comprised of a plurality of parallel floor members that form elongated troughs or valleys with sloped sides to trap falling abrasive and waste particles. Between each pair of adjacent floor members and extending below their lower edges is a duct member having an elongated opening which is periodically closeable by a controllable closure means such as an inflatable valve member that provides an airtight seal. At one end of the floor the ducts have small permanent openings to permit air to enter and their other ends are connected to a suction fan capable of creating a conveying air velocity in the ducts when the closure means has closed. During operation of the blast-room the closure means remains open for a period of time while a quantity of abrasive and waste particles are collected in the conveying ducts, then periodically the duct closure means are closed so that the conveying air can remove the particles from the ducts.

15 Claims, 9 Drawing Figures PA'TENTEnJum m2 SHEET 10F 4 INVENTOR. TED A. ARNOLD ATTORNEYS PATENTEDJum 1m SHEET 2 OF 4 INVENTOR. TED A. ARNOLD ATTORNEYS' PATENTEnJum 1972 3,672,292 sum 3 or 4 ue u? INVENTOR. TED A. ARNOLD ATTORNEYS PNENTEDJum 1972 3. 67 2 292 SHEET u or 4 T0 DUST Z COLLECTOR T0 DUST 22 COLLECTOR 24 To 142- SEPARATOR m v 402 l 1 I 4O 34 FIG 6 v/ F G 7 INVENTOR. I00 96 TED A. ARNOLD AIR PRESSURE ATTORNEYS m, W Lm...

BLAST-ROOM FOR ABRASIVE BLASTING SYSTEM This invention relates to abrasive blasting systems and more particularly to an improved blast-room floor for collecting and removing spent abrasive and waste particles so that the abrasive can be separated and recovered for recycling in the system.

In the abrasive blasting field so-called pitless or shallow pit type blast-rooms have been used extensively to facilitate the surface treatment of articles by abrasive particles and also provide means to recover and clean the spent abrasive so that it can be reused. Heretofore, such blast-rooms, as described in U.S. Pat. Nos. 2,839,339; 2,912,918 and 3,026,789 utilized floor structures with a plurality of small hoppers for trapping the falling abrasive with openings in the hoppers communicating with adjacent ducts through which the abrasive could pass. The openings between the hoppers and ducts were permanently open and in some instances it was necessary to vary their size to provide the most efficient removal of the abrasive. A suction force applied to the ends of the ducts created a constant downdraft throughout the blast-room and also provided the necessary conveying velocity in the floor ducts. One of the problems with the aforesaid system was that in order to maintain a constant downdraft ventilation and also an air velocity in the ducts sufficient to convey the abrasive, a relatively large amount of power was required. Also, the downdraft ventilation had some inherent disadvantages. Heretofore, cross ventilation was only possible in blast-rooms utilizing'a mechanical or vibratory conveying system for the spent abrasive, but such vibratory systems are practical only for relatively coarse abrasive. Thus, prior to the present invention no blast-rooms using relatively fine abrasives such as glass-beads were capable of utilizing cross ventilation with its inherent advantages instead of downdraft ventilation.

Therefore, one object of the present invention is to solve the aforesaid problem by providing a blast-room with cross ventilation and a separate air suction system for scavenging ducts in the floor.

Another object of the present invention is to provide a blastroom with floor ducts that can be temporarily closed before a suction force is applied to create an air flow in the ducts sufficient to remove collected abrasive particles and waste material.

Yet another object of the present invention is to provide a blast-room system that will operate with a considerably reduced horsepower requirement, and with air conveying and dust collection apparatus and equipment of less size and cost, as compared with comparable blast-rooms of the prior art.

Still another object of the present invention is to provide an improved blast-room ducted floor structure that is easy to service and maintain and has a unique construction particularly well adapted for ease and economy of manufacture.

These and other important objects of my invention are accomplished by an abrasive blasting system having a blast-room floor comprised of elongated floor members forming troughs or recesses with sloped sides that will trap falling abrasive particles and debris. The floor members are spaced apart to form elongated openings into conveying ducts extending below. As blasting takes place within the blast-room, abrasive and waste particles that fall onto the floor members flow through the openings into the ducts. Each opening for a duct is provided with a controllable closure means which is actuated to close and seal the opening so that a suction fan can produce an airflow through the ducts that will remove the collected abrasive and waste particles therein. Actuation of the closure means may be initiated at randomly selected times or it may be controlled by an automatic cycling device set at the rate required to keep the ducts relatively clean. Since this arrangement eliminates the need for downdrafi ventilation within the blastroom, effective dust removal therein is accomplished by a simple, inexpensive cross draft means connected to and controlled by conventional dust apparatus forming of the system.

An important advantage of my blast-room floor ducting construction is that it eliminates the need for a concentrator in this type of abrasive blasting system. This is because the abrasive being recovered falls by gravity within the floor ducts and is not combined with and therefore does not have to be extracted from the ventilating air for the blast-room. This feature reduces considerably the complexity and expense of the present system.

Other objects, advantages and features of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawing, in which:

FIG. I is a view in perspective showing an abrasive blasting system according to the present invention with portions broken away to show the blast-room floor;

FIG. 2 is a enlarged view in perspective and in section showing the blast-room floor for the system of FIG. 1 in greater detail;

FIG. 3 is a fragmentary view in elevation and in section showing one duct for the blast-room floor of FIG. 2 as it appears in the open position;

FIG. 3A is a view similar to FIG. 3 showing the floor duct in the closed position;

FIG. 4 is a view in elevation and in section showing a modified form of blast-room floor duct according to the present invention;

FIG. 5 is a view in elevation and in section of another modified form of blast-room floor duct according to my invention;

FIG. 5A is a view similar to FIG. 5 showing the floor duct in the closed position;

FIG. 6 is a fragmentary view in elevation and in section showing the blast-room for the system of FIG. 1; and

FIG. 7 is a fragmentary plan view in section taken along line 7-7 of FIG. 6.

Referring to the drawing, FIG. 1 shows an abrasive blasting system embodying the principles of the present invention and comprising a blast-room 10 having a ducted floor 12 for trapping spent abrasive particles and waste debris so that they can be conveyed from the floor and separated for reuse. The blast-room may be any suitable enclosure made from strong, durable materials forming end walls 14, side walls 16, and a roof 18. In the example shown, one side wall has a pair of access doors 20 large enough to allow an operator and the article being treated to enter the room. A series of baffled inlet openings 22 for taking outside air into the room are provided along one end wall 14 and on the opposite end wall 14a are outlets 24, as shown in FIG. 6, which are connected to a pair of dust removal ducts 26 and 28. These ducts extend to a conventional dust collector 29 having a fan 31 and bag filter, wet precipitator or other apparatus (not shown) for separating dust from the air. Thus, the dust separator fan provides the suction necessary to maintain a continuous cross draft flow of air across the blast-room.

The blast-room floor has an upper perforated grating 30 or the like for supporting the blasting apparatus and the objects to be blasted. Below this perforated supporting member are a series of trough-like recesses 32 that trap the spent abrasive and debris, and below these recesses are duct members 34 through which the abrasive and debris are conveyed. As will be seen by the detailed description that follows, the passage of abrasive and debris particles from each trough-like recess through an opening 36 to its duct below is controlled by a valve means 38, so that only periodically is a conveying air velocity established within the ducts. Along one side of the blast-room, as seen best in FIG. 7, the outlet ends of all the ducts 34 are connected in parallel to a common pickup duct 40. This latter duct extends to a cyclone type separator 42 of the well known type that is mounted just below a suction fan 44. Within the separator, the reusable spent abrasive is removed from the air, light waste particles and dust which would contaminate it. This spent abrasive falls downwardly through a reclaimer 46 and into a fluidizing pot or blast generator 48 before being recycled into a blast hose 50 for reuse. The waste particles, air and dust are carried upwardly from the separator to the previously described dust collector 29 which also filters the cross-ventilating air.

Turning to FIG. 2, the ducted floor of the blast-room, as shown in greater detail, comprises a plurality of pairs of elongated members 52 and 54 that may readily be formed from sheet metal. When placed together these members have an inverted V-shaped cross section and are supported underneath by internal braces or, as shown, by a solid concrete filler 56. Both members have a narrow flange at their top which together form a flat ridge 58 for supporting the perforated member 30 of the floor. From the upper flange each member has a main surface that slopes downwardly at an angle (e.g. 45) to a point where it bends to form a lower vertical wall 62. At the lower edge of this vertical wall is a horizontally extending flange 64. These horizontal flanges of adjacent members 52 and 54 are spaced apart but connected together by a strip member 66.

In the embodiment of FIGS. 2 and 3, the vertical wall 62 of one member 52 is higher than the vertical wall 63 of the other member 54. Fitted within the space between adjacent floor members is the duct member 34 which is a four sided element preferably made of sheet metal and having an irregular shaped cross section. A horizontal bottom 70 of this duct member bears directly against and may be fastened to the connecting strip 66. A vertical side 72, which is perpendicular to the bottom side, lies parallel to the higher vertical wall member 62 of the member 52. An upper flange member 74 forms an acute angle with and extends downwardly from the upper edge of the vertical side 72. This flange is connected through one flange of an angle member 76 to a plate 78 that is adjacent to and is sloped downwardly from the lower edge of the sloped member 52 at the same angle thereof. The lower edge of the plate 78 is located at a fixed distance from the top edge of the vertical wall 63 on the opposite member 54 thereby forming an elongated opening 36 into the duct 34 having a uniform width. Another side portion 80 of the duct member 34 extends upwardly from the horizontal bottom 70 of the conveying duct and abuts against the upper edge of the vertical wall 63 of the adjacent floor member 54. The angle member 76 which is fixed between the sloping plate 78 and the upper angular flange 74 of the duct has a right angle flange 82 that is spaced from the lower duct side 80. Fixed to this right angle flange is an elongated valve or sealing means 38 that is movable outwardly in one direction along its length to bear against the lower duct side 80 and thereby close the opening 36 into the duct. In the embodiment shown, the sealing means 38 is an elongated inflatable member made of elastomeric material of a type that is commercially available. Generally, it has a relatively thick base portion 84 that lies flush against and is secured to the right angle flange 82 of the member 76 by fastening means such as screws or a suitable adhesive. Integral with the base portion of the sealing member are foldable side portions 88 that connect to opposite sides of an outer head portion 90. The latter may have an outer yieldable surface formed with a plurality of grooves that will form an air-tight seal when pressed against a flat surface. The base member, side portions and top portion of each sealing member form an elongated cavity 92 which is closed at one end. The other ends of all the sealing members are connected to a controllable source of air pressure so that they can be inflated and deflated. As shown in FIG. 3A, when each sealing member is inflated its top portion 90 extends and engages the duct side 80 to form a seal along it and prevent air or abrasive from falling into the duct.

As shown diagrammatically in FIG. 7, the inlet ends of all of the inflatable sealing members 38 are connected to an air line 94 that is connected to a constant compressed air source 96 through a valve 98. The valve is controlled by a suitable timer device 100 that will periodically operate to open and close the valve. A relief valve is provided in the air line 94 to prevent applying excessive pressure to the inflatable sealing members 38.

In normal operation, as blasting takes place within the blastroom 10, the spent abrasive and waste particles fall by gravity to the floor 12, through the grating 30 and into the elongated troughs 32. When the sealing members 38 are retracted or open", the abrasive and waste particles continue to fall through the elongated openings and into the duct members. In accordance with an important feature of the present invention the abrasive enters each duct member 34 near its bottom and the duct members is shaped so that it can never be filled and blocked by abrasive. Due to the flow characteristics of the abrasive, the size and shape of the duct, as previously described, and the size of the opening, only a limited amount of abrasive will flow into the duct, and when it reaches its angle of repose, it then starts to fill the recess or trough above the duct. When this occurs, it is time to evacuate or scavenge the duct to remove the abrasive collected and make room for more from the trough above. Generally, time for the valve is set so that the sealing members will inflate and the ducts will be scavenged often enough to prevent any appreciable buildup of abrasive in the trough-like recesses between the floor members. For example, in a typical blast-room having around 10 ducts, all of the inflatable sealing members will operate at approximately l0-l5 psi to inflate simultaneously, thereby closing their respective ducts. The sealing members will remain closed for the preset period (eg 30 seconds) during which time the abrasive will be conveyed from the ducts. Thereafter the sealing members will be deflated for 5 to 10 seconds to allow abrasive collected in the troughs above the ducts to drop into them before the next conveying cycle commences.

As shown in FIG. 7, the ends of the ducts have inlet openings 102 located against an end wall 14 and preferably under a baffle 104 to provide for an influx of conveying air through the ducts. As previously mentioned, the amount of abrasive that can possibly flow into each duct is limited and cannot exceed a level that would block the duct and reduce the rate of air flow below an efiicient conveying velocity. Thus, with the sealing members closed, and the suction fan 44 in operation, the conveying air flow through the ducts quickly scavenges the abrasive and waste particles and moves it through the pickup duct 40 directly to the separator 42 and reclaimer 46 where they are separated in the usual manner.

In FIGS. 5 and 5A, a somewhat modified floor 12a for my blast-room is shown. Here, adjacent floor members 52a are similarly shaped in cross section each with a sloping surface having a vertical wall portion 62a extending downward along its lower edge. These vertical wall portions of adjacent floor members are spaced apart to form a cavity for a duct member 34a between them. This duct member comprises a pair of channel-like members 106, each having a web portion that slopes at the same angle as the members 52a towards the center of the duct. One relatively wide flange 108, along one side of the web portion, fits against a vertical wall portion 620 of the spaced apart floor members. 0n the inner edge of each channel member 106 is a narrower flange 110 and these flanges are spaced apart to form an elongated opening 36a. Below this opening is an inverted channel member 112 having opposite flanges 114 which are attached and sealed to the channel flanges 108 to form the duct member 344. When servicing is required the entire duct member can be easily removed from the cavity between the floor members. This, of course, is true also with the duct member 34 in the embodiment of FIGS. 3 and 3A.

The joints or seams 116 between the channel members 106 and the sloping floor members 520 are preferably filled with a caulking compound so that the sloping surface will be continuous and smooth from the ridge of the floor members to the opening 360. Spaced apart along the channel members 106 are a series of horizontal cross braces 117 that support an elongated stringer 118 which is located directly above the opening 36a. A triangular shaped deflector member 120 is mounted on top of the stringer so that abrasive will not collect on it but will fall into the opening below. Attached to the underside of the stringer by a suitable fastening means is a sealing member 38a which may be like the member 38 previously described, that is, controllable by air pressure to inflate and extend to a sealing position. With this sealing member, however, it is preferred that its outer head portion 90a be somewhat cylindrical in shape with a diameter larger than the width of the opening 36a. Thus, as shown in FIG. 5A, when the sealing member for each duct member 34a is inflated, the cylindrical head end will seat in its opening and provide an airtight seal.

FIG. 4 shows another modified form of floor 12b for a blastroom embodying the principles of my invention. Here, each pair of adjacent floor members 52b forming a trough slope directly to an interconnecting horizontal strip 122 that supports a central vertical member 124. Thus, each two floor members 52b forming a trough in this embodiment can be made from one sheet of sheet metal. Along the top edge of this central member is an angular deflector member 126 that slopes in opposite directions towards the adjacent floor mem bers 52b. Both lower edges of this deflector member terminate at a distance from the adjacent floor member, thereby forming elongated openings 36b on both sides of the deflector member. Fixed to each leg of the deflector member near its lower edge is an elongated bracket member I28 to which is attached a sealing member 38b which may be similar to the one shown in FIG. 3. These sealing members are located so that when retracted, as shown in FIG. 4, the openings 3612 are left fully open. When inflated, the outer portion of both sealing members extend to and engage the floor members 52b, thereby forming two air-tight ducts 34b beneath the angular deflector member 1265. Operation of this floor is thus the same as with the other floor constructions except that two sealing members are used for each trough-like recess between adjacent floor members. This construction allows the troughs of a blast-room floor to be somewhat shallower for an equivalent distance between ridges of the troughs. This arrangement thus requires less volume for the floor under the blast-room.

While I have described the various blast-room floor constructions of my invention using the inflatable, flexible sealing members 38, it should be understood that other sealing means for periodically closing the duct openings such as mechanical, movable sealing devices could be utilized within the scope of the invention.

From the foregoing it should be apparent that the present invention provides an improved blast-room abrasive blasting system that provides a ventilating system separate from the abrasive or grit conveying system. For most blast-room configurations it reduces the volume of air flow required for the system thereby providing a substantial saving in size and cost of equipment, particularly for the dust collector, the main suction fan and the motor driving it. My system is particularly adaptable for large rectangular rooms where certain air speeds are required for satisfactory ventilation, since these speeds can be accomplished with a much lower air flow rate with cross ventilation than with downdraft ventilation as used in prior systems.

The present invention not only provides a system with greater operating efficiency but also provides one that is less expensive to manufacture. The blast-room floor may be as sembled from relatively few components and the fabrication and installation of a plurality of hopper members is not required as in previous floor constructions. Moreover, the need for a separate concentrator is eliminated because the ventilating air is not combined with the conveying air.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. In an abrasive blasting system that provides for the surface treatment of articles and the recovery of the abrasive par- 75 ticles used in the blasting operation, the combination comprismg:

a blast-room having side walls and an access door;

a floor for said blast-room including means forming a series of elongated recesses, means extending below said recesses forming a series of air ducts, means forming an elongated opening between each said recess and a said air duct so that spent abrasive trapped in said recesses can flow into the ducts, and controllable closure means for periodically closing said openings between said recesses and their air ducts;

and means operable when said closure means have closed said openings for causing air to flow through said ducts at a rate sufficient to convey abrasive material from them.

2. The system as described in claim 1 including means for causing a constant cross draft through said blast-room for removing dust therefrom.

3. The system as described in claim 2 wherein said latter means for causing a cross draft comprises a series of inlets to ambient air on one side wall of the blast-room, outlet means on the opposite side of the blast-room from said inlets, a dust collector means having a suction fan, and duct means interconnecting said outlet means with said dust collecting means.

4. The system as described in claim 1 wherein said recesses and said air ducts are elongated and said closure means comprises an elongated inflatable sealing member for each said opening between a recess and an air duct, and controllable air pressure means for inflating said sealing members to close said openings, when said air ducts are to be scavenged.

5. The system as described in claim 4 including valve means connected to said air pressure means and timer means for operating said valve means and thereby actuating said sealing members at a predetermined rate.

6. The system as described in claim 1 wherein said means for causing air flow through said ducts comprises a suction fan on a reclaimer means providing a suction sufiicient to create a conveying air velocity through said ducts.

7. A blast-room for an abrasive blasting system including a ducted floor structure for recovering abrasive particles used in the surface treatment or articles in the room, comprising:

side and end walls extending upwardly from said floor structure;

means on said floor forming trough-like recesses with sloping sides;

duct means extending below each trough-like recess with an elongated opening between each recess and its duct means to allow spent abrasive and waste particles to fall into the duct means;

and elongated movable sealing means extending along each said opening for periodically closing said opening between each said recess and its duct means; and means connected to one side of said floor structure for conveying air through the duct means lengthwise when said openings are cleared to remove the collected abrasive and waste particles therein.

8. The blast-room as described in claim 7 wherein said recesses are formed from a plurality of floor members forming elongated troughs having generally a triangular shaped cross section;

means for supporting said floor members in a parallel spaced apart arrangement;

means forming an air duct between adjacent, spaced apart floor members including a sloping cover member forming a narrow elongated opening into the air duct below and extending along said recess;

an elongated, inflatable sealing member mounted on said cover member and extendable, when inflated, to engage the opposite side of the duct means and thereby seal said elongated opening for substantially its entire length.

9. The blast-room as described in claim 7 wherein said recesses comprise a plurality of floor members forming elongated troughs having generally a triangular shaped cross section;

a perforated flooring means extending over and supported by said floor members;

an elongated deflector member mounted in each trough having an inverted V-shaped cross section and, forming a duct below, said deflector member having lower edges spaced from adjacent floor members to form openings to the duct;

elongated inflatable sealing members attached to opposite sides of said deflector member, said sealing members each having an outer movable portion that engages and seals against the adjacent floor member when the sealing member is actuated.

10. The blast-room as described in claim 7 wherein said recesses comprise a plurality of floor members forming elongated troughs having generally a triangular shaped cross section, said duct means being located between adjacent said floor members and including cover means having a central, elongated opening into each said duct;

support means in each said trough located directly above said duct opening;

and an elongated inflatable sealing member attached to said support means for temporarily closing said opening when abrasive material is to be conveyed by air from the duct below.

11. In a blast-room for an abrasive blasting system including side walls and a roof, a ducted floor between the side walls for recovering spent abrasive particles from operating within the blast room, said floor comprising:

a plurality of floor members fonning trough-like recesses with sloping sides and an elongated cavity along the bottom of each recess;

a removable duct member within each said cavity with an elongated opening provided a passage from each recess to its duct member for spent abrasive particles that fall into the recess;

and elongated movable sealing means for periodically closing each said opening so that conveying air can flow through said duct members lengthwise to remove abrasive and waste particles collected therein.

12. The blast-room floor as described in claim 11 wherein said floor members have vertical walls with pairs of floor members forming the cavity between them, a said duct member within each said cavity being made of sheet metal and bent to form said opening along one side thereof, said sealing means comprising an inflatable, flexible sealing member which is movable upon inflation to close said opening.

13. The blast-room floor as described in claim 11 wherein said floor members are in pairs and have vertical wall portions of equal height forming a cavity between them, each said duct member within a cavity comprising upper surfaces that slope toward a central opening;

support means located about said duct member, and an inflatable, sealing member mounted on said support means and extendable downwardly to close said duct opening.

14. The blast-room floor as described in claim 11 wherein said floor members have a V-shaped cross section which forms each said recess of the floor, a support means extending upwardly along the center of each recess and deflector means with sloping portions extending toward the opposite sloping sides of its said floor member, and an extendable, elongated sealing member mounted on each sloping portion of said deflector means.

15. The blast-room floor as described in claim 11 wherein each said duct member has an irregular shaped cross section with said elongated opening into said duct member being located well below its top portion so that abrasive and waste particles flowing into the duct member can never fill it or block the flow of conveying air through the duct member. 

1. In an abrasive blasting system that provides for the surface treatment of articles and the recovery of the abrasive particles used in the blasting operation, the combination comprising: a blast-room having side walls and an access door; a floor for said blast-room including means forming a series of elongated recesses, means extending below said recesses forming a series of air ducts, means forming an elongated opening between each said recess and a said air duct so that spent abrasive trapped in said recesses can flow into the ducts, and controllable closure means for periodically closing said openings between said recesses and their air ducts; and means operable when said closure means have closed said openings for causing air to flow through said ducts at a rate sufficient to convey abrasive material from them.
 2. The system as described in claim 1 including means for causing a constant cross draft through said blast-room for removing dust therefrom.
 3. The system as described in claim 2 wherein said latter means for causing a cross draft comprises a series of inlets to ambient air on one side wall of the blast-room, outlet means on the opposite side of the blast-room from said inlets, a dust collector means having a suction fan, and duct means interconnecting said outlet means with said dust collecting means.
 4. The system as described in claim 1 wherein said recesses and said air ducts are elongated and said closure means comprises an elongated inflatable sealing member for each said opening between a recess and an air duct, and controllable air pressure means for inflating said sealing members to close said openings, when said air ducts are to be scavenged.
 5. The system as described in claim 4 including valve means connected to said air pressure means and timer means for operating said valve means and thereby actuating said sealing members at a predetermined rate.
 6. The system as described in claim 1 wherein said means for causing air flow through said ducts comprises a suction fan on a reclaimer means providing a suction sufficient to create a conveying air velocity through said ducts.
 7. A blast-room for an abrasive blasting system including a ducted floor structure for recovering abrasive particles used in the surface treatment or articles in the room, comprising: side and end walls extending upwardly from said floor structure; means on said floor forming trough-like recesses with sloping sides; duct means extending below each trough-like recess with an elongated opening between each recess and its duct means to allow spent abrasive and waste particles to fall into the duct means; and elongated movable sealing means extending along each said opening for periodically closing said opening between each said recess and its duct means; and means connected to one side of said floor structure for conveying air through the duct means lengthwise when said openings are cleared to remove the collected abrasive and waste particles therein.
 8. The blast-room as described in claim 7 wherein said recesses are formed from a plurality of floor members forming elongated troughs having generally a triangular shaped cross section; means for supporting said floor members in a parallel spaced apart arrangement; means forming an air duct between adjacent, spaced apart floor members including a sloping cover member forming a narrow elongated opening into the air duct below and extending along said recess; an elongated, inflatable sealing member mounted on said cover member and extendable, when inflated, to engage the opposite side of the duct means and thereby seal said elongated opening for substantially its entire length.
 9. The blast-room as described in claim 7 wherein said recesses comprise a plurality of floor members forming elongated troughs having generally a triangular shaped cross section; a perforated flooring means extending over and supported by said floor members; an elongated deflector member mounted in each trough having an inverted V-shaped cross section and, forming a duct below, said deflector member having lower edges spaced from adjacent floor members to form openings to the duct; elongated inflatable sealing members attached to opposite sides of said deflector member, said sealing members each having an outer movable portion that engages and seals against the adjacent floor member when the sealing member is actuated.
 10. The blast-room as described in claim 7 wherein said recesses comprise a plurality of floor members forming elongated troughs having generally a triangular shaped cross section, said duct means being located between adjacent said floor members and including cover means having a central, elongated opening into each said duct; support means in each said trough located directly above said duct opening; and an elongated inflatable sealing member attached to said support means for temporarily closing said opening when abrasive material is to be conveyed by air from the duct below.
 11. In a blast-room for an abrasive blasting system including side walls and a roof, a ducted floor between the side walls for recovering spent abrasive particles from operating within the blast room, said floor comprising: a plurality of floor members forming trough-like recesses with sloping sides and an elongated cavity along the bottom of each recess; a removable duct member within each said cavity with an elongated opening provided a passage from each recess to its duct member for spent abrasive particles that fall into the recess; and elongated movable sealing means for periodically closing each said opening so that conveying air can flow through said duct members lengthwise to remove abrasive and waste particles collected therein.
 12. The blast-room floor as described in claim 11 wherein said floor members have vertical walls with pairs of floor members forming the cavity between them, a said duct member within each said cavity being made of sheet metal and bent to form said opening along one side thereof, said sealing means comprising an inflatable, flexible sealing member which is movable upon inflation to close said opening.
 13. The blast-room floor as described in claim 11 wherein said floor members are in pairs and have vertical wall portions of equal height forming a cavity between them, each said duct member within a cavity comprising upper surfaces that slope toward a central opening; support means located about said duct member, and an inflatable, sealing member mounted on said support means and extendable downwardly to close said duct opening.
 14. The blast-room floor as described in claim 11 wherein said floor members have a V-shaped cross section which forms each said recess of the floor, a support means extending upwardly along the center of each recess and deflector means with sloping portions extending toward the opposite sloping sides of its said floor member, and an extendable, elongated sealing member mounted on each sloping portion of said deflector means.
 15. The blast-room floor as described in claim 11 wherein each said duct member has an irregular shaped cross section with said elongated opening into said duct member being located well below its top portion so that abrasive and waste particles flowing into the duct member can never fill it or block the flow of conveying air through the duct member. 